Correlated Reference-Assisted Variational Quantum Eigensolver.

Area of Science:

• Quantum chemistry
• Computational physics
• Quantum computing

Background:

• Variational Quantum Eigensolver (VQE) is a hybrid quantum-classical algorithm for finding molecular ground-state energies.
• Current VQE methods often require significant quantum resources, limiting their applicability.
• Active-space approximations aim to reduce computational cost by focusing on relevant electrons.

Purpose of the Study:

• To develop a novel active-space approximation for VQE.
• To reduce the quantum computational resources required for VQE calculations.
• To improve the accuracy of VQE by including electron correlation effects.

Main Methods:

• Utilized a double exponential unitary coupled-cluster ansatz and downfolding technique.
• Derived an effective Hamiltonian incorporating a correlated potential from one-body second-order Møller-Plesset perturbation theory (OBMP2).
• Employed canonical transformation and cumulant approximation for correlated potential calculation.

Main Results:

• The proposed active-space approximation significantly reduces quantum resource requirements.
• The method accurately predicts energies and density matrices (via dipole moment) for systems with singlet and doublet ground states.
• Demonstrated superior performance compared to active-space VQE with a Hartree-Fock reference.

Conclusions:

• The developed active-space approximation offers a more resource-efficient and accurate approach to VQE.
• This method effectively captures electron correlation, enhancing VQE performance.
• The approach shows promise for accurate quantum chemistry simulations on near-term quantum devices.